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Month: September 2015

Researchers identify neurons that can abruptly halt a planned behavior

Date:

September 17, 2015

Source:

Johns Hopkins University

Summary:

Scientists have identified the precise nerve cells that allow the brain to make a split-second change of course, like jamming on the brakes.

Johns Hopkins University researchers, working with scientists at the National Institute on Aging, have revealed the precise nerve cells that allow the brain to make this type of split-second change of course. In the latest issue of the journal Nature Neuroscience, the team shows that these feats of self-control happen when neurons in the basal forebrain are silenced.

“The study discovered a new role for basal forebrain neurons in the control of action,” said Michela Gallagher, the Krieger-Eisenhower Professor of Psychology and Neuroscience at Johns Hopkins. “This work opens the door to novel approaches focused on this circuit in certain neurological and psychiatric conditions that affect basic cognitive functions of the brain.”

The ability to rapidly stop a behavior is critical for everyday functioning — allowing people crossing the street to freeze if a car surprises them, to not reach for their phone when it vibrates in their pocket during a meeting or, in the case of a batter, to stop from swinging at a bad pitch. A better understanding of the cognitive mechanics behind what’s known as reactive inhibition could help people suffering from neurological conditions where such control is diminished — everything from Alzheimer’s disease and Parkinson’s disease to attention deficit hyperactivity disorder and normal aging.

Scientists had assumed the ability to stop a planned behavior occurred in the basal ganglia, an area in the brain responsible for a variety of motor control functions including the ability to start an action or a behavior. This study demonstrates, however, that the stop response happens in the basal forebrain, a part of the brain best known for regulating sleep, but also recognized as a site for early neurodegeneration in Alzheimer’s disease.

The researchers trained rats to play a game: If the rats quickly moved after hearing a tone, they got a treat. The rats were also rewarded if they stopped moving when a light flashed. All the while, the team monitored the rats for electrical signals in the basal forebrain.

The researchers trained rats to move quickly to get a treat. After hearing a tone, the rats would rush into a new port to lick sucrose water. But, when the tone was followed by a flash of light, the rats would have to immediately stay in place to get a treat. In other words, when the light flashed, the rule of reward reversed — instead of moving quickly to get reward, the rats had to cancel that planned response and stay still to get their treat.

While the rats performed the tasks, the team monitored the activity of individual basal forebrain neurons. The researchers were also able to get the rats to stop without using the flash of light by stimulating the same neurons with a small pulse of electricity.

“In the lab, we were able to manipulate these neurons, which caused rats to stop their behavior even though they had no reason to do so,” said lead author Jeffrey D. Mayse, who conducted the research as a Johns Hopkins doctoral student and is now a postdoctoral fellow at Brown University.

“Understanding how these cells are involved in this form of self-control expands our knowledge of the normal brain circuits involved in everyday decision-making,” he said, “and will be absolutely critical to developing future treatments and therapies for diseases and disorders with impaired reactive inhibition as a symptom.”

Summary:Fluctuating hormone levels change a woman’s social behaviour over the course of the menstrual cycle. Mood swings and irritability before the period as well as a greater interest in sex during ovulation are well known. Now psychologists have discovered that the willingness to share one’s own resources with strangers also fluctuates with hormone levels. Women exhibit a higher willingness to cooperate during and shortly after menstruation — this is the result of two online studies involving over 400 German and US American women.

To qualify for the study, the participants had to have a natural menstrual cycle, in other words not be using hormone-based contraceptives, had to not be pregnant and not have entered menopause yet. The researchers compared the willingness to cooperate between women in the time during and shortly after menstruation (early follicular phase), when the levels of the hormones estrogen and progesterone are low, and a few days after ovulation (midluteal phase), when the estrogen and progesterone levels are especially high. The hormone levels were estimated based on the self-reported day in the cycle.

The researchers measured the subjects’ individual willingness to cooperate using a well-established psychological scale, the “Social Value Orientation.” To do so, they asked the women to divide fictitious money between themselves and another person who was a complete stranger to them.

“Numerous studies have shown that people who exhibit a high willingness to share in this test also donate money more often and in larger amounts in real life, take the train instead of the car to work more often and are more willing to compromise in negotiations than people with a less pronounced pro-social value orientation,” Christine Anderl, lead author of the study, explains.

The two studies showed that the women were significantly more inclined to share their own resources with a stranger during and shortly after menstruation than they were a few days after ovulation.

The greater the cycle-dependent level of the “female” sex hormone estrogen, the lower the willingness to share of the women on a purely statistical basis. “While we are firmly convinced that the variation in the willingness to share over the course of the cycle is a real and systematic effect, we still have to determine whether or not it is really caused by estrogen as the present data suggest,” Christine Anderl tells us.

“This matches the findings of other research groups, who were able to show that hormones such as oxytocin and the “male” sex hormone testosterone affect the willingness to cooperate in humans,” Prof. Sabine Windmann from the Institute for Experimental Psychology 2 at the Goethe University commented. How strongly the cycle-dependent fluctuations in the willingness to cooperate affect the day-to-day life of women and which areas of life are particularly affected by this will have to be researched in further studies.

However, the researchers have already found initial evidence which suggests that the described effects also occur when the subjects are using real money. These results are also interesting in light of hormonal contraception. Little is currently known about how synthetic hormones act on the receptors in the brain and what effect they have on the behaviour of women.

Summary:Juries in criminal cases typically decide if someone is guilty, then a judge determines a suitable level of punishment. New research confirms that these two separate assessments of guilt and punishment — though related — are calculated in different parts of the brain. In fact, researchers have found that they can disrupt and change one decision without affecting the other.

New work by researchers at Vanderbilt University and Harvard University confirms that a specific area of the brain, the dorsolateral prefrontal cortex, is crucial to punishment decisions. Researchers predicted and found that by altering brain activity in this brain area, they could change how subjects punished hypothetical defendants without changing the amount of blame placed on the defendants.

“We were able to significantly change the chain of decision-making and reduce punishment for crimes without affecting blameworthiness,” said René Marois, professor and chair of psychology at Vanderbilt and co-principal author of the study. “This strengthens evidence that the dorsolateral prefrontal cortex integrates information from other parts of the brain to determine punishment and shows a clear neural dissociation between punishment decisions and moral responsibility judgements.”

The research titled “From Blame to Punishment: Disrupting Prefrontal Cortex Activity Reveals Norm Enforcement Mechanisms” was published on Sept. 17 in the journal Neuron.

The Experiment

The researchers used repetitive transcranial magnetic stimulation (rTMS) on a specific area of the dorsolateral prefrontal cortex to briefly alter activity in this brain region and consequently change the amount of punishment a person doled out.

“Many studies show the integrative function of the dorsolateral prefrontal cortex in relatively simple cognitive tasks, and we believe that this relatively basic process forms the foundation for far more complex forms of behavior and decision-making, such as norm enforcement,” said lead author Joshua Buckholtz, now an assistant professor of psychology at Harvard.

The researchers conducted experiments with 66 volunteer men and women. Participants were asked to make punishment and blameworthiness decisions in a series of scenarios in which a suspect committed a crime. The scenarios varied by harm caused (ranging from property loss to grievous injury and death) and how culpable the suspect was for the act (fully responsible or not, due to mitigating circumstances.) Half of the subjects received active rTMS while the other half of the subjects received a sham or placebo version of rTMS.

Level of Harm

Across all participants and all trials, both culpability and level of harm were significant predictors of the amount of punishment the subjects deemed appropriate. But subjects receiving active rTMS chose significantly lower punishments for fully culpable suspects than did those subjects receiving sham rTMS, particularly in scenarios that resulted in low to moderate harm. Additional analyses suggested that the effect was due to impaired integration of signals for harm and culpability.

“Temporarily disrupting the dorsolateral prefrontal cortex function appears to alter how people use information about harm and culpability to render these decisions. In other words punishment requires that people balance these two influences, and the rTMS manipulation interfered with this balance, especially under conditions in which these factors are dissonant, such as when the intent is clear but the harm outcome is mild,” said Buckholtz.

Implications

The research team’s main goal in this work is to expand the knowledge of how the brain assesses and then integrates information relevant to guilt and punishment decisions. It will also advance the burgeoning interdisciplinary study of law and neuroscience.

“This research gives us deeper insights into how people make decisions relevant to law, and particularly how different parts of the brain contribute to decisions about crime and punishment. We hope that these insights will help to build a foundation for better understanding, and perhaps one day better combatting, decision-making biases in the legal system,” said co-author Owen Jones, professor of law and biological sciences at Vanderbilt and director of the MacArthur Foundation Research Network on Law and Neuroscience.

Story Source:

The above post is reprinted from materials provided by Vanderbilt University. The original item was written by Amy Wolf. Note: Materials may be edited for content and length.

Summary:A new study based on longitudinal data confirms a college degree provides an advantage in lifetimes earnings, but a related decision once students make it to college could prove to be even more crucial as STEM majors earn roughly $700,000 more over 40 years than social science or humanities majors.

The study that includes a University of Kansas researcher found large lifetime earnings gaps depending on a student’s field of study. For examples, men who major in science, technology, engineering and mathematics, or STEM fields, and earning a bachelor’s degree achieved roughly $700,000 to $800,000 higher 40-year lifetime earnings from ages 20 to 59 than social science or liberal arts majors.

“That means the decision for whether for you going to college versus what kind of major you want to study, the latter decision is more important for your lifetime earnings,” said Kim, a KU associate professor of sociology and the study’s lead author.

Social science or liberal arts majors with a bachelor’s degree in social science or liberal arts majors still earn $400,000 more than high school graduates, but gaining an advanced degree in social science does not raise lifetime earnings substantially compared to a bachelor’s degree in the same major, the study found.

Kim said the study is meant to show the labor-market differentials across field of study because there is little research right now in this area. However, the researchers don’t dispute there are other benefits to earning a liberal arts or humanities degree.

“When you are educated, you have a better lifestyle. You can maybe enjoy more complicated books, so you have more engaging or more interesting conversations with value,” Kim said. “There is a whole other benefit of education. A liberal arts education is good, but it doesn’t necessarily transform into a high salary.”

Surprisingly, men who have a college degree in an education major earn only $46,000 over 40 years compared to high school graduates. When a 4 percent annual discount rate is applied for future earnings, the lifetime value of college degree for some majors compared to a high school degree turns out to be slightly negative.

The journal Sociology of Education recently published the article “Field of Study in College and Lifetime Earnings in the United States” online, and the study will appear in the October edition of the journal Sociology of Education.

This is the first study to use nationally representative survey data matched to longitudinal earnings data spanning a long stretch of the same person’s life to document how lifetime earnings vary by field of study and how lifetime earnings change by getting an advanced degree in different fields. Past studies had relied on either one year or a limited number of years of data with projections and did not estimate the effect of field of study on lifetime earnings for those who have an advanced degree.

The researchers examined Social Security Administration personal income tax data to follow the earnings of the same individuals over 20 years and then estimated the long-term effects of fields of study for U.S. men and women. The study included three measures of lifetime earnings: gross lifetime earnings by majors; net lifetime earnings after accounting for demographic and high school performance related factors; and net present value at age 20 after applying a 4 percent discount rate.

Kim said the overall findings likely aren’t surprising because engineering and professional jobs that require STEM or business degrees do gain higher economic returns in the open market. However, he said the degree of difference in earnings suggested the horizontal stratification in education across field of study appears to be more consequential than the usual focus on vertical stratification, which refers to the earnings gap between levels of education.

For one, it illuminates the importance of foregoing some earnings, especially in your 20s while attending graduate school, especially for students in majors that wouldn’t typically earn high returns over their lifetime. Attending graduate school in the social sciences or liberal arts added much less earnings than a graduate student in a professional field, for example.

“The reason why going to graduate school is not going to be very beneficial for some majors in terms of financing is to get the degree you need to spend your time in school for an extended period of time. That’s time you’re not going to be working. Even though you earn more after getting a degree, it is not enough to substantially raise your lifetime earnings,” Kim said.

However, the findings could be key in two other areas: examining the effects of gender on earnings and economic inequality.

Related to gender, college degrees no matter the field of study seem to benefit women with higher earnings compared with women who only graduated high school. For men in some fields of study, the earnings return would not be as high as a woman over her high school counterparts.

“This is not because college-educated women earn more than equally educated men,” Kim said, “but because labor market opportunities for less educated women are so scarce.”

Also, other studies have found that students from less-educated families tend to flock more to STEM fields or others with higher earnings returns than students of educated parents, who might be more inclined to choose a liberal arts degree.

“This kind of major choice we have is one mechanism to actually reduce economic inequality,” he said.

A reduced fear of humans can be the driving force behind the characteristics that have developed since wild animals became domesticated, according to research by ethologists.

About 8,000 years ago we began to domesticate animals — a process that fundamentally changed the way animals and people live. Domesticated animals of today have characteristics that distinguish them from their wild ancestors, including size, colour, reproduction and behaviour.

In a fresh study the LiU researchers show that many of these changes can have been driven by a simple fact: the animal populations that humans selected to domesticate grew increasingly tame. The study is now published in Biology Letters.

The researchers used a population of red junglefowl (Gallus gallus), the wild ancestor of all domesticated fowl. For five generations they selected animals with a congenital reduced fear of humans, and bred their offspring. For comparison, they also bred a separate line from the fowl that were most fearful of humans.

“We used a standardised behaviour test where we studied the fowl’s reaction to a human. This method resembled the conditions during the very first stage of fowl husbandry 8,000 years ago,” says Beatrix Agnvall, doctoral student in ethology and first author of the article.

After just five generations, the increasingly tame fowl had developed a higher metabolism and feed conversion rate — they grew more although they ate less than the more fearful animals in the control group. They were also more cautious in situations where humans were not involved, and, as in previous studies of the same animals, they laid larger eggs. The levels of the hormone serotonin were higher in the tame roosters, and the researchers believe that this can be one of the mechanisms driving the results.

According to Per Jensen, professor of ethology at LiU and head of the study, increased tameness was an important prerequisite in the animals’ ability to live with humans.

“The results show that it can automatically have led to many of the characteristics that we and our ancestors liked about domesticated animals. Therefore we can suppose that our ancestors didn’t necessarily select animals because they were good at producing food, but mainly because they were easy to manage,” says Prof Jensen, who believes the results could also apply to other domesticated animals like pigs, sheep and cattle.

Key move to grass-based foods was 400,000 years earlier than previously known

Date:

September 15, 2015

Source:

Johns Hopkins University

Summary:

Pre-humans’ shift toward a grass-based diet took place about 400,000 years earlier than experts previously thought, providing a clearer picture of a time of rapid change in conditions that shaped human evolution.

Millions of years ago, our primate ancestors turned from trees and shrubs to search for food on the ground. In human evolution, that has made all the difference.

The shift toward a grass-based diet marked a significant step toward the diverse eating habits that became a key human characteristic, and would have made these early humans more mobile and adaptable to their environment.

New evidence just published by a research team led by a Johns Hopkins University scientist shows that this significant shift took place about 400,000 years earlier than experts previously thought, providing a clearer picture of a time of rapid change in conditions that shaped human evolution.

Naomi E. Levin, the lead author of the report just published in Proceedings of the National Academy of Sciences, said the diet shift is one of an array of changes that took place during the Pliocene era — 2.6 million to 5.3 million years ago — when the fossil record indicates human ancestor species were starting to spend more time on the ground walking on two feet. Understanding the timing of these events can help show how one change related to another.

“A refined sense for when the dietary changes took place among early humans, in relation to changes in our ability to be bipedal and terrestrial, will help us understand our evolutionary story,” said Levin, an assistant professor in the Department of Earth and Planetary Sciences.

The paper reports on an analysis of fossil teeth found in Ethiopia that shows the shift from a diet based on trees and shrubs to one that included grass-based foods took place about 3.8 million years ago — roughly 400,000 years earlier than the date supported by previous research. (Grass-based foods could include not only grasses and their roots, but also insects or animals that ate grass.)

The shift in eating habits would have broadened our ancestors’ horizons and improved their species’ capacity for survival, Levin said.

“You can then range wider,” Levin said of the human precursors, species including Australopithecus afarensis, extinct some 3 million years ago and represented most famously in the fossil informally known as “Lucy.” “You can be in more places, more resilient to habitat change.”

“This research reveals surprising insights into the interactions between morphology and behavior among Pliocene primates,” said co-author Yohannes Haile-Selassie of the Cleveland Museum of Natural History. “The results not only show an earlier start to grass-based food consumption among hominins and baboons but also indicate that form does not always precede function. In the earliest baboons, dietary shift toward grass occurred before its teeth were specialized for grazing.”

Researchers analyzed 152 fossil teeth from an array of animals including pigs, antelopes, giraffes and human ancestors gathered from a roughly 100 square-mile area of what is now the Afar region of Ethiopia. Among the samples were teeth from hominins — including contemporary humans and our extinct ancestors — believed to represent 16 different individuals, said Levin, one of four co-authors of the paper. Her collaborators were Haile-Selassie, Stephen R. Frost of the University of Oregon and Beverly Z. Saylor of Case Western Reserve University.

The teeth were examined for carbon isotope distribution, a marker that can distinguish the types of foods the animals ate. The data showed that both human ancestors and members of a now-extinct, large species of baboon were eating large amounts of grass-based foods as early as 3.76 million years ago. Previous research dated the earliest evidence for grass-based foods in early human diets to about 3.4 million years ago.

The researchers could not firmly establish a link between external environmental change and the diet of hominins and baboons, but instead attribute the dietary expansion to changes in relations among members of the African primate communities, such as the appearance of new species of primates.

“Timing is critical to understanding the context for this dietary expansion among early humans in relationship to what’s happening in global climate, in vegetation communities in Africa, among other mammals, and in terms of the other evolutionary changes that are happening among early humans,” she said. “If we know the timing of events we can start to relate them to one another.”

Summary:A new technique to selectively and noninvasively turn on groups of neurons in worms could be boon to science and medicine.

Salk scientists have developed a new way to selectively activate brain, heart, muscle and other cells using ultrasonic waves. The new technique, dubbed sonogenetics, has some similarities to the burgeoning use of light to activate cells in order to better understand the brain.

This new method–which uses the same type of waves used in medical sonograms–may have advantages over the light-based approach–known as optogenetics–particularly when it comes to adapting the technology to human therapeutics. It was described September 15, 2015 in the journal Nature Communications.

“Light-based techniques are great for some uses and I think we’re going to continue to see developments on that front,” says Sreekanth Chalasani, an assistant professor in Salk’s Molecular Neurobiology Laboratory and senior author of the study. “But this is a new, additional tool to manipulate neurons and other cells in the body.”

In optogenetics, researchers add light-sensitive channel proteins to neurons they wish to study. By shining a focused laser on the cells, they can selectively open these channels, either activating or silencing the target neurons. But using an optogenetics approach on cells deep in the brain is difficult: typically, researchers have to perform surgery to implant a fiber optic cable that can reach the cells. Plus, light is scattered by the brain and by other tissues in the body.

Chalasani and his group decided to see if they could develop an approach that instead relied on ultrasound waves for the activation. “In contrast to light, low-frequency ultrasound can travel through the body without any scattering,” he says. “This could be a big advantage when you want to stimulate a region deep in the brain without affecting other regions,” adds Stuart Ibsen, a postdoctoral fellow in the Chalasani lab and first author of the new work.

Chalasani and his colleagues first showed that, in the nematode Caenorhabditis elegans, microbubbles of gas outside of the worm were necessary to amplify the low-intensity ultrasound waves. “The microbubbles grow and shrink in tune with the ultrasound pressure waves,” Ibsen says. “These oscillations can then propagate noninvasively into the worm.”

Next, they found a membrane ion channel, TRP-4, which can respond to these waves. When mechanical deformations from the ultrasound hitting gas bubbles propagate into the worm, they cause TRP-4 channels to open up and activate the cell. Armed with that knowledge, the team tried adding the TRP-4 channel to neurons that don’t normally have it. With this approach, they successfully activated neurons that don’t usually react to ultrasound.

So far, sonogenetics has only been applied to C. elegans neurons. But TRP-4 could be added to any calcium-sensitive cell type in any organism including humans, Chalasani says. Then, microbubbles could be injected into the bloodstream, and distributed throughout the body–an approach already used in some human imaging techniques. Ultrasound could then noninvasively reach any tissue of interest, including the brain, be amplified by the microbubbles, and activate the cells of interest through TRP-4. And many cells in the human body, he points out, can respond to the influxes of calcium caused by TRP-4.

“The real prize will be to see whether this could work in a mammalian brain,” Chalasani says. His group has already begun testing the approach in mice. “When we make the leap into therapies for humans, I think we have a better shot with noninvasive sonogenetics approaches than with optogenetics.”

Both optogenetics and sonogenetics approaches, he adds, hold promise in basic research by letting scientists study the effect of cell activation. And they also may be useful in therapeutics through the activation of cells affected by disease. However, for either technique to be used in humans, researchers first need to develop safe ways to deliver the light or ultrasound-sensitive channels to target cells.

Other researchers on the study were Stuart Ibsen and Ada Tong of the Salk Institute, and Carolyn Schutt and Sadik Esener of the University of California, San Diego.

The work and the researchers involved were supported by a Salk Institute Pioneer Fund Postdoctoral Fellowship, a Salk Institute Innovation Grant, the Rita Allen Foundation, the W.M. Keck Foundation and the National Institutes of Health.

Story Source:

The above post is reprinted from materials provided by Salk Institute. Note: Materials may be edited for content and length.

Summary:Evidence of emotional load sharing between partners in a close relationship has bee uncovered by researchers. Their new study found that a strong relationship with a loved one can help ease stress when placed in difficult situations.

“We wanted to test a new evolutionary theory in psychology called Social Baseline Theory which suggests that humans adapted to be close to other humans,” says Ms. Lougheed. “The idea is that individuals function at a relative deficit when they are farther away from people they trust.”

In their study, Ms. Lougheed and co-authors measured the stress levels of 66 adolescent girls during a spontaneous speech task. Before the speech performance, the participants and their mothers rated the quality of their relationship. During the speeches, researchers tracked the participants’ level of stress via galvanic skin response (measuring the level of skin perspiration). To account for the effect of physical — rather than purely emotional — closeness, the participants’ mothers were instructed either to hold or not hold their daughters’ hand.

The researchers found that physical closeness allowed the participants to manage their stress more efficiently, regardless of how close the mother-daughter pair reported being. However, when physical contact was removed from the equation, only the participants who reported higher relationship quality showed signs of load sharing.

“Our results suggest that we are better equipped to overcome challenging situations when we are closer — either physically or in terms of how we feel in our relationships — to people we trust,” says Ms. Lougheed.

Participants who had reported the lowest level of mother-daughter relationship closeness and lacked physical contact during the task were the least efficient in managing emotional stress.

“We were somewhat surprised to find that mothers’ stress did not vary by physical closeness — after all, it can be stressful for parents to watch their children perform, but being able to offer physical comfort might have lessened the mothers’ stress,” says Ms. Lougheed.

“Thus, emotional load sharing in this context was not a function of the mothers’ stress level, and we expect that it occurred instead through the daughters’ perceptions of how stressful it was to give a speech. That is, higher physical and/or relationship closeness helped the daughters feel like they could overcome the challenging situation.”

The results suggest that physical contact can overcome some difficulties associated with relatively low relationship quality, or that being in a high-quality relationship is helpful for managing emotions in the same way as the physical comfort of a loved one. Lougheed does, however, note that the general level of relationship quality was relatively high in their sample, and that physical contact may function very differently in distressed families. She also cautions against generalizing these results to other partnerships — such as a relationship between romantic partners, platonic friends and other family members — and suggest that more research be done to determine the effect of socioeconomic status and gender, amongst other factors.

The study, “Sharing the burden: the interpersonal regulation of emotional arousal in mother-daughter dyads,” was published in the journal Emotion.

Summary: Humans are extremely choosy when it comes to mating, only settling down after a long screening process involving nervous flirtations, awkward dates, humiliating rejections and the occasional lucky strike. But evolution is an unforgiving force — isn’t this choosiness rather a costly waste of time and energy when we should just be ‘going forth and multiplying?’ What, if anything, is the evolutionary point of it all? A new study may have the answer.

Doing a cost/benefit analysis of love is a challenging business, with many potential confounds, and — in the case of humans — some ethical limitations on doing experiments. A new study publishing on September 14th in the Open Access journal PLOS Biology by Malika Ihle, Bart Kempenaers, and Wolfgang Forstmeier from the Max Planck Institute for Ornithology, Seewiesen, Germany, describes an elegant experiment designed to tease apart the consequences of mate choice.

The authors took advantage of the fact that the zebra finch shares many characteristics with humans, mating monogamously for life, and sharing the burden of parental care. Female finches choose mates in a way that is specific to the individual, and there is little consensus among females as to who the cutest male is.

Using a population of 160 birds, the authors set up a speed-dating session, leaving groups of 20 females to choose freely between 20 males. Once the birds had paired off, half of the couples were allowed to go off into a life of wedded bliss. For the other half, however, the authors intervened like overbearing Victorian parents, splitting up the happy pair, and forcibly pairing them with other broken-hearted individuals.

Bird couples, whether happy or somewhat disgruntled, were then left to breed in aviaries, and the authors assessed couples’ behavior and the number and paternity of dead embryos, dead chicks and surviving offspring.

Strikingly, the final number of surviving chicks was 37% higher for individuals in chosen pairs than those in non-chosen pairs. The nests of non-chosen pairs had almost three times as many unfertilized eggs as the chosen ones, a greater number of eggs were either buried or lost, and markedly more chicks died after hatching. Most deaths occurred within the chicks’ first 48 hours, a critical period for parental care during which non-chosen fathers were markedly less diligent in their nest-care duties.

Watching the couples’ courtship showed some noticeable differences — although non-chosen males paid the same amount of attention to their mates as the chosen ones did, the non-chosen females were far less receptive to their advances, and tended to copulate less often. An analysis of harmonious behavior revealed that non-chosen couples were generally significantly less lovey-dovey than the chosen ones. There was also a higher level of infidelity in birds from non-chosen pairs — interestingly the straying of male birds increased as time went by while females roamed less.

Overall the authors conclude that birds vary rather idiosyncratically in their tastes, and choose mates on the basis that they find them stimulating in some way that isn’t necessarily obvious to an outside observer. This stimulation “turns on” the females to increase the likelihood of successful copulation and encourages paternal commitment for the time needed to raise young; together these maximize the couple’s likelihood of perpetuating their genes through their thriving offspring.

Sounds familiar? This is presumably what the human dating game is about, the need perhaps exacerbated by the extended phase of dependence during which our children need parental support. Indeed, these authors’ results are consistent with some studies on the differences between love-based and arranged marriages in human society.

Story Source:

The above post is reprinted from materials provided by PLOS. Note: Materials may be edited for content and length.

Summary:Scientists have discovered a new species of hominin, a small creature with a tiny brain that opens the door to a new way of thinking about our ancient ancestors.

An international team of scientists, including one from the University of Colorado Denver and another from the University of Colorado Anschutz Medical Campus in Aurora, announced the discovery Thursday of a new species of hominin, a small creature with a tiny brain that opens the door to a new way of thinking about our ancient ancestors.

The discovery of 15 individuals, consisting of 1,550 bones, represents the largest fossil hominin find on the African continent.

“We found adults and children in the cave who are members of genus Homo but very different from modern humans,” said CU Denver Associate Professor of Anthropology Charles Musiba, PhD, who took part in a press conference Thursday near the discovery inside the Rising Star Cave in the Cradle of Humankind World Heritage Site outside Johannesburg, South Africa. “They are very petite and have the brain size of chimpanzees. The only thing similar we know of are the so-called `hobbits’ of Flores Island in Indonesia.”

Homofloresiensis or Flores Man was discovered in 2003. Like this latest finding, it stood 3.5 five feet high and seems to have existed relatively recently though the exact age is unknown.

Caley Orr, PhD, an assistant professor of cell and developmental biology at the University of Colorado School of Medicine, analyzed the fossil hands.

“The hand has human-like features for manipulation of objects and curved fingers that are well adapted for climbing,” Orr said. “But its exact position on our family tree is still unknown.”

The new species has been dubbed Homo naledi after the cave where it was found — naledi means `star’ in the local South African language Sesotho.

One of the most intriguing aspects of the discovery is that the bodies appear to have been deposited in the cave intentionally. Scientists have long believed this sort of ritualized or repeated behavior was limited to humans.

The team of 35 to 40 scientists was led by Lee Berger, research professor in the Evolutionary Studies Institute at the University of Witwatersrand in South Africa. It was supported by the National Geographic Society and the National Research Foundation. The October issue of National Geographic magazine will feature the discovery as its cover story. It will also be the subject of a NOVA/National Geographic Special airing Sept. 16.

Getting inside the Dinaledi chamber of the remote cave system was difficult, requiring the help of six `underground astronauts,’ who squeezed through a 7-inch wide gap to reach the remains.

“The chamber has not given up all of its secrets,” said Berger, a National Geographic Explorer-in-Residence. “There are potentially hundreds if not thousands of remains of H. naledi still down there.”

The announcement coincides with the publication of two studies about the new species in the journal eLife, co-authored by Musiba and Orr.

In it, the researchers try to place Homonaledi in context with other species. Generally speaking, they say, there is an assumption that any new group of fossils must belong to an existing species.

But it’s not that simple here.

“Assigning these remains to any known species of Homo is problematic,” the study said. “While Homo(naledi) shares aspects of cranial and mandibular morphology with Homohabilis, Homorudolfensis, Homoerectus, MP Homo and Homosapiens, it differs from all of these taxa in its unique combination of derived cranial vault, maxillary, and mandibular morphology.”

The study suggests that Homonaledi most closely resembles Homoerectus with its small brain and body size. Yet it also resembles Australopithecus which highlights its own uniqueness.

Complicating matters is the fact that researchers still don’t know the exact age of the fossil site.

“If these fossils are late Pliocene or early Pleistocene, it is possible that this new species of small-brained, early Homorepresents an intermediate between Australopithecus and Homoerectus,” the study said.

That would also make the new species very old.

But if the fossils are more recent, they theorize, it raises the possibility that a small-brained Homolived in southern Africa at the same time as larger brained Homospecies were evolving.

“This raises many questions,” Musiba said. “How many species of human were there? Were their lines that simply extended outward and then disappeared? Did they co-exist with modern humans? Did they interbreed?”

Homonaledi has a chest similar to a chimpanzee and hands and feet proportionate with modern humans, though with curved fingers.

“They would have had great climbing ability,” said Musiba. “The oldest adults were about 45 and the youngest were infants.”

He described poring over the bones late at night as akin to `hitting the jackpot.’

“You just didn’t want to go home because it was so exciting,” he said. “I felt like a kid in a candy store.” The find represents another milestone in Musiba’s efforts to advance the understanding of our earliest human relatives.

As director of CU Denver’s Tanzania Field School, he takes groups of students each year to gain hands-on experience working in and around the famed Laetoli hominin footprints site and Olduvai Gorge where some of the oldest hominin remains have been found.

Not long ago, they discovered ancient footprints of lions, rhinos and antelopes near those of the early hominins.

And last year, Musiba was appointed to an international team of advisors dedicated to building a museum complex in Tanzania to showcase a collection of 70 hominin footprints, estimated at 3.6 million years old. They are considered the earliest example of bipedalism among hominins.

Musiba said the Rising Star expedition was notable for getting so many anthropologists to work together.

“Anthropology can be a cut-throat profession with all these scientists scrambling for limited resources,” he said. “To me one of the most exciting aspects of this research was the collaborative nature of it.”